ATLANTA (RNN) – The Centers for Disease Control reports a nasty stomach bug has affected almost 300 people in nine states with scattered reports of outbreaks in two others. It is apparently spreading.

The intestinal illness called cyclospora infection is caused by a one-cell parasite invisible to the naked eye. It takes about a week to incubate then causes intense diarrhea, loss of appetite, weight loss, stomach cramps and pain, bloating, nausea and fatigue.

Vomiting and body aches are also associated with infection, and it is common to feel extremely tired, according to the CDC.

The outbreak in the U.S. appears to have started in Iowa about mid-June. The other outbreaks are primarily in Midwestern states, though cases have been confirmed in Georgia.

Untreated symptoms can last from a few days to a month and may go away for a while before returning. People catch it by ingesting water or food that has been contaminated with feces passed by a person who is already infected.

People who think they have been infected should see their doctor immediately. The treatment usually involves heavy doses of antibiotics and drinking plenty of water.

As of Wednesday, 18 people have been hospitalized in three states with the disease. No particular food items have been identified as the cause, and it's not clear if the outbreaks in the different states are connected.

The CDC's investigation is ongoing and it is working with multiple local health departments and the U.S. Food and Drug Administration.

Here are a list of the states where outbreaks have been confirmed: Iowa, Nebraska, Texas, Wisconsin, Georgia, Connecticut, New Jersey, Minnesota and Ohio.

Illinois and Kansas have also notified CDC of one case each that may have been acquired out of state.